In the field of aqueous dispersion including a functional material, there are known functional materials, for example, agricultural chemicals such as a herbicide or an insecticide, pharmaceuticals such as an anticancer agent, an antiallergy agent or an anti-inflammation agent, a coloring material such as an ink or a toner containing a colorant. Recently, digital printing technologies are showing remarkable progresses. Such digital printing technologies, represented by so-called electrophotographic technology and ink jet recording technology, are becoming more and more important as an image forming technology in the offices and at homes.
Among such technologies, the ink jet technology, being a direct recording technology, has significant features of compactness and a low electric power consumption. Also it recently shows a rapid improvement in the image quality due, for example, to a formation of finer nozzles. An example of the ink jet technology is a method of heating an ink, supplied from an ink tank, with a heater in a nozzle, thereby inducing an evaporation and a bubble formation, thus discharging the ink and forming a record on a recording medium. Another example is a method of generating a vibration in a piezoelectric element, thereby discharging the ink.
The ink employed in these methods is generally an aqueous solution of a dye, and hence there may take place a bleeding when plural colors are superposed or so-called feathering phenomenon, along a direction of fibers of paper in a recorded portion of the recording medium. For avoiding these drawbacks, U.S. Pat. No. 5,085,698 discloses a use of an ink composed of a pigment dispersion. However, there are in fact desired various improvements on such existing technologies.